Magnetic drum

The magnetic drum was invented by G. Taushek in 1932 in Austria on the basis of a principle discovered by Pfleumer.
Taushek put a ferromagnetic layer on the outside of a metal drum. Read and write heads were mounted at a distance of some micrometers that produced an electro magnetic pulse. This pulse could be stored by changing the magnetic orientation of the ferro magnetic particle the write head passed over at that very moment.
Thus binary values of 0 or 1 are recorded by generating electric pulses while the drum is rotating. The magnetic field of some of the particles suspended are polarized along a "track".
Reading back the recording is done by detecting which particle was "polarized" and which was not, and thus representing the binary "1-s" and "zero's" The capacity of a drum of 20 cm long and 10 cm in diameter was about 500.000 bit.
Each track had its own read and write head.

Drum memory was an early form of computer memory that was widely used in the 1950s and into the 1960s. For many machines, a drum formed the main working memory of the machine, with data and programs being loaded on to or off of the drum using media such as paper tape or punch cards. Drums were later replaced by core memory, which was faster and had no moving parts, and which lasted until semiconductor memory entered the scene.

Related Topics:
Magnetic tape

References:
http://www.yorku.ca/sasit/sts/sts3700b/lecture16a.html
http://www.thocp.net/timeline/1927.htm